Highly selective recognition of mercury ions through the “naked-eye”

A new sensor 2-((E)-(3-(1H-imidazol-1-yl)propylimino)methyl)-5-(diethylamino)phenol (1) based on the combination of diethylaminosalicylaldehyde and imidazole groups was designed and synthesized as a Hg2 + selective colorimetric chemosensor. Upon treatment of 1 with mercury ions, sensor 1 showed a color-change from colorless to yellow in a mixture of H2O/DMF (5:95), while many other ions such as Al3 +, Zn2 +, Cd2 +, Cu2 +, Fe2 +, Mg2 +, Cr3 +, Ag+, Co2 +, Ni2 +, Na+, K+, Ca2 +, Mn2 + and Pb2 + had no influence. Notably, this chemosensor could distinguish clearly Hg2 + from Cu2 +, Ag+, Fe2 + and Pb2 +. The underlying signaling mechanism is a ligand-to-metal charge-transfer (LMCT) process. Compound 1 showed the serial formation of the 1:1 and the 1:2 complexation between 1 and Hg2 +. This two-step binding mode was proposed based on the UV titration, 1H NMR titration and ESI-mass studies.